An Experimental Investigation of Partially Premixed Combustion Strategies Using Multiple Injections in a Heavy-Duty Diesel Engine 2006-01-0917

Optimizations were performed on a single-cylinder heavy-duty Caterpillar SCOTE 3401E engine for NOx, PM and BSFC reductions. The engine was equipped with a Caterpillar 300B HEUI fuel injection system capable of up to four injections with timings from 90 BTDC to 90 ATDC. The engine was operated at a medium load (57%), high speed (1737 rev/min) operation point.

A micro-genetic algorithm was utilized to optimize a hybrid, double-injection strategy, which incorporated an early, premixed pilot injection with a late main injection. The fuel injection parameters, intake boost pressure, and EGR were considered in the optimization. The optimization produced a parameter set that met the 2007 and 2010 PM emissions mandate of 0.0134 g/kW-hr, and was within the 1.5x not to exceed NOx + HC mandate of 2.694 g/kW-hr.

Following the optimization exercise, further parametric interaction studies were performed to reveal the underlying interactions and phenomena. These interaction studies led to a modified parameter set that allowed full compliance to the 2007 emissions mandates. A triple injection study utilizing the previous hybrid double injection work with an additional close-coupled post injection was then undertaken to explore the merits of close-coupled post injections. These studies revealed that close-coupled post injections could offer a slight decrease in PM levels for constant NOx + HC and BSFC levels. Using this strategy with a small level of EGR resulted in NOx + HC emissions below the 0.8 × 2007 mandates, however the PM levels were higher than the mandated limit. Finally, a quadruple injection strategy was evaluated, which added an additional pilot injection to the previous triple injection strategy. This split-pilot strategy with close-coupled post injection resulted in PM levels below the 0.8 × 2007 mandates, however, the NOx emissions were outside of 2007 emissions compliance.